Human ventilatory response to 8 h of euoxic hypercapnia.
Ventilation (VE) rises throughout 40 min of constant elevated end-tidal PCO2 without reaching steady state (S. Khamnei and P. A. Robbins. Respir. Physiol. 81: 117-134, 1990). The present study investigates 8 h of euoxic hypercapnia to determine whether VE reaches steady state within this time. Two protocols were employed: 1) 8-h euoxic hypercapnia (end-tidal PCO2 = 6.5 Torr above prestudy value, end-tidal PO2 = 100 Torr) followed by 8-h poikilocapnic euoxia; and 2) control, where the inspired gas was air. VE was measured over a 5-min period before the experiment and then hourly over a 16-h period. In the hypercapnia protocol, VE had not reached a steady state by the first hour (P < 0.001, analysis of variance), but there were no further significant differences in VE over hours 2-8 (analysis of variance). VE fell promptly on return to eucapnic conditions. We conclude that, whereas there is a component of the VE response to hypercapnia that is slow, there is no progressive rise in VE throughout the 8-h period.
Tansley
J G
JG
University Laboratory of Physiology, University of Oxford, United Kingdom.
Pedersen
M E
ME
Clar
C
C
Robbins
P A
PA
D000293:Adolescent; D000328:Adult; D002245:Carbon Dioxide / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010100:Oxygen / Q000502:physiology*; D010313:Partial Pressure; D012123:Pulmonary Ventilation / Q000502:physiology*; D013990:Tidal Volume
D002245:Carbon Dioxide; D010100:Oxygen